Porositized carbon is considered a carbon material with a high amount of pores. Activated carbon is a main commercial product of the porositized carbon. Activated carbon is a crude form of graphite with a random or amorphous structure, which is highly porous with large internal surface area, exhibiting a broad range of pore sizes from visible cracks or crevices to slits of molecular dimensions. Generally, activated carbon has a surface area in excess of 500 m2/g as determined by the gas adsorption testing. In the adsorption analysis, non-polar gases, e.g. N2, CO2, Ar, CH4, etc., are used, and the N2 adsorption at 77 K is widely used.1 
In the early 20th century, powder activated carbon was produced using wood as a raw material. With further development, different types of the conventional powder activated carbon have been produced, including granular activated carbon, pelletized activated carbon, and etc. These types of activated carbon allow for easy recycling and waste minimization. The feedstocks for activated carbons include coconut shells, wood char, and lignin, among other materials.1 
Activation methods can be divided into two categories: (1) physical/thermal activation; and (2) chemical activation. Physical/thermal activation uses a mild oxidizing gas, e.g. CO2, water steam, etc., to eliminate the bulk of the volatile matters, followed by partial gasification. This method gives materials with higher porosity and more surface area than the chemical activation method.1 The chemical activation method employs chemicals (such as acid, strong base, or salt) to increase the surface area.2 The chemical activators for the activated carbon include potassium hydroxide (KOH)3, sodium hydroxide (NaOH)4, nitric acid (HNO3)5, sulfuric acid (H2SO4)6, hydrochloric acid (HCl)7, hydrogen peroxide (H2O2)8, zinc chloride (ZnCl2)9, phosphoric acid (H3PO4)10, potassium carbonate (K2CO3)11, potassium phosphate dibasic (K2HPO4)12, and cobalt acetate (Co(OAc)2).13 
Thermal activation can used for the activated carbon processed from biomass, such as wood, agriculture stems, and any other lignocellulosic based resources. Usually, the conventional thermal activation method is to use a mild oxidizing gas CO2, including two steps, 1) carbonization with flowing inert gas, and 2) activation by CO2. For instance, the biomass pyrolysis process happens at a pyrolysis temperature (e.g. 700° C.), followed by an activation process at a higher temperature (e.g. 800° C.) with flowing CO2 as an activating gas. During the carbonization process, the inert gas flow is used, and so that the generated gas components (including the CO2) due to the material decomposition are removed. During the activation process, usually at higher temperature, the additional CO2 can be introduced to initiate the activation process.
Mozammel et al. (2002)15 reported that activated carbon sales were estimated at 375,000 tons in 1990, not including the Eastern Europe and China. Sales could be over 450,000 tons if Eastern Europe and China were included. By late 1990s, the production of the activated carbon was estimated at about 700,000 tons/year, with a market growth of about 4-6%/year. In the Freedonia Group's report in 2012, “World Activated Carbon to 2016”,16 the activated carbon demand worldwide is expected to increase more than ten percent per year to 1.9 million metric tons in 2016. The large market demand will contribute to the high gross sales. The global activated carbon market was about $1.8 billion in 2011 and was estimated to reach $3.0 billion by 2016.